FIG. 11 shows a conceptual configuration of a conventional liquid-development electrophotographic apparatus. As shown in FIG. 11, the conventional liquid-development electrophotographic apparatus has an intermediate transfer member 51 formed of a roller which is rotated at a predetermined speed; and a backup roller 59 which is in press contact with the intermediate transfer member 51 and is rotated such that a contact portion of the backup roller 59 and a contact portion of the intermediate transfer member 51 move in the same direction. An image formed of liquid toner on the surface of the intermediate transfer member 51 is transferred to a printing medium 60, which is moved while being nipped between the intermediate transfer member 51 and the backup roller 59.
An image to be transferred to the printing medium 60 from the intermediate transfer member 51 consists of a yellow element image, which is in yellow toner and transfer-supplied from a developing unit 54; a red element image, which is in red toner and transfer-supplied from a developing unit 55; a blue element image, which is in blue toner and transfer-supplied from a developing unit 56; and a black element image, which is in black toner and transfer-supplied from a developing unit 57.
The developing unit 54, which transfer-supplies a yellow element image to the intermediate transfer member 51, includes a toner supply pot 54d for storing a yellow liquid toner; a pattern roller 54c for taking out the liquid toner from the toner supply pot 54d; a developing roller 54b for leveling the liquid toner supplied from the pattern roller 54c so as to form a toner layer of uniform thickness; and a photoconductor drum 54a for forming a yellow element image by use of the toner layer transfer-supplied from the developing roller 54b. 
The yellow liquid toner stored in the toner supply pot 54d is supplied in a state of including a carrier, which is a nonvolatile liquid. Thus, the carrier, which is a nonvolatile liquid, adheres to the surface of the intermediate transfer member 51 on which a yellow element image is formed.
Subsequently to being transfer-supplied with a yellow element image, the intermediate transfer member 51 is similarly transfer-supplied with a red element image from the developing unit 55. Then, the intermediate transfer member 51 is sequentially transfer-supplied with a blue element image from the developing unit 56, and a black element image from the developing unit 57, thereby forming a color image as a whole.
Each of the developing unit 55, the developing unit 56, and the developing unit 57 assumes a configuration similar to the aforementioned configuration of the yellow-related developing unit 54. Accordingly, a color image is formed on the surface of the intermediate transfer member 51 by means of yellow liquid toner, red liquid toner, blue liquid toner, and black liquid toner; and a carrier contained in the color toners adheres to the surface of the intermediate transfer member 51.
Although unillustrated in FIG. 11, the surface of the photoconductor drum associated with each of the colors is equipped with, for example, an image formation mechanism for electrostatically forming a latent image, and an accessory mechanism therefor; a mechanism for eliminating static electricity from the surface of the photoconductor drum after transfer-supply of the corresponding element image to the intermediate transfer member 51; and a mechanism for removing residual toner.
When an image formed on the surface of the intermediate transfer member 51 passes a position of contact with a carrier-removing unit 58, the carrier is removed from the image. Then, the image—which is formed of the color toners—is transferred to the printing medium 60, which moves while being nipped under pressure between the backup roller 59 and the intermediate transfer member 51. The image transferred to the printing medium 60 is fixed in a fixing unit (not shown).
After passing a position of transfer to the printing medium 60, a portion of the intermediate transfer member 51 on which an image is previously formed reaches the position of a cleaning unit 52. The cleaning unit 52 removes residues of toner (hereinafter, called “residual toner” or “residual developer”), whereby the intermediate transfer member 51 prepares for a next cycle of forming images in the corresponding colors by means of the developing units 54, 55, 56, and 57.
The conventional cleaning unit 52 shown in FIG. 11 will be described in detail with reference to FIG. 12. The cleaning unit 52 includes a blade 52a which is in press contact with the intermediate transfer member 51, and a residual-toner pot 52b. The blade 52a scrapes off residual toner of firm adhesion from the surface of the intermediate transfer member 51, thereby collecting the residual toner in the residual-toner pot 52b. 
FIG. 13 shows another conventional cleaning unit. As shown in FIG. 13, the cleaning unit 52 includes an electrically conductive elastic-body roller 62a in press contact with the intermediate transfer member 51, and an elastic cleaning blade 62b disposed downstream of the roller 62a. The electrically conductive elastic-body roller 62a is grounded, or a bias voltage opposite in polarity to an electrostatic latent image is applied to the electrically conductive elastic-body roller 62a. Specifically, a bias voltage polarized in such a direction as to cause exfoliation of residual toner is applied between the electrically conductive elastic-body roller 62a and the intermediate transfer member 51 to thereby exfoliate from the intermediate transfer member 51 residual toner—which coheres/firmly adheres to the intermediate transfer member 51. The elastic cleaning blade 62b is adapted to remove, from the intermediate transfer member 51, the residual toner which is exfoliated from the intermediate transfer member 51 by means of the elastic-body roller 62a. 
Usually, a 4-color image formed on the intermediate transfer member 51 is not entirely transferred to a printing medium. Residual developer (residual toner) which remains on the intermediate transfer member 51 without being transferred to the printing medium is removed in a period of time ranging from the end of a transfer process in which the intermediate transfer member 51 makes one rotation to thereby transfer a toner image to the printing medium, to the start of a subsequent process in which a toner image is transferred from a photoconductor drum to the intermediate transfer member 51. In other words, the residual developer is removed by means of the cleaning unit located upstream of the developing unit 54 and downstream of the backup roller 59, which is disposed in opposition to the intermediate transfer member 51 provided for transferring a toner image to the printing medium.
However, in an ordinary image formation operation, residual toner subjected to a cleaning operation of the cleaning unit is a residue of toner left in transfer of a toner image to the printing medium 60. Thus, the quantity of adhering residual toner is small, but the residual toner adheres firmly to the intermediate transfer member 51. The above-described conventional configuration fails to completely remove such a firmly adhering residual toner.
Furthermore, in the course of repetition of an image formation operation, residual toner which the cleaning unit 52 has failed to collect gradually accumulates and begins to mix in an image formed on the surface of the intermediate transfer member 51, thereby affecting the quality of an image which the intermediate transfer member 51 forms. Meanwhile, for example, when a printing medium is not supplied because of a certain error, most of an image formed on the surface of the intermediate transfer member 51 is subjected to a cleaning operation as residual toner. In such a case, the cleaning operation must handle a large amount of residual toner. Thus, the operation mode of the liquid-development electrophotographic apparatus must be changed over to a cleaning mode for removing residual toner.
Thus, when the number of image formation operations of the liquid-development electrophotographic apparatus reaches a predetermined value or when the liquid-development electrophotographic apparatus suffers an error which requires a recovery operation accompanied by cleaning, an operator changes over the operation mode of the apparatus to a cleaning mode and causes the apparatus to perform the cleaning operation a predetermined number of times, thereby preventing deterioration in the quality of an image formed by means of the intermediate transfer member 51.
Such a conventional cleaning-mode operation to be performed by a liquid-development electrophotographic apparatus will be described with reference to FIGS. 14 and 15. A configuration required for description of a control procedure will be described with reference to the block diagram of FIG. 14. An arithmetic control section B50 contained in a liquid-development electrophotographic apparatus B05 fetches a required program segment from a control program stored in a control program section B58 and executes a predetermined control procedure.
A printing drive section B51 includes a drive system for driving the intermediate transfer member 51, and a press-contact drive system for driving the backup roller 59. An image formation section B52 includes drive systems for driving the corresponding developing units 54, 55, 56, and 57, and a drive system for driving the carrier-removing unit 58.
An error detection section B55 reports to the arithmetic control section B50 signals obtained from various error detection sensors disposed in the liquid-development electrophotographic apparatus B05.
A printing control section B56a specifies an operation which the printing drive section B51 is to perform, timing of performing the operation, and the like; and a development control section B56b specifies an operation which the image formation section B52 is to perform, timing of performing the operation, and the like.
Control procedure will be described with reference to the flowchart of FIG. 15. For example, when the number of image formation operations performed by the liquid-development electrophotographic apparatus B05 reaches a predetermined value, or when the liquid-development electrophotographic apparatus B05 suffers an error which requires a recovery operation accompanied by cleaning, the liquid-development electrophotographic apparatus B05 indicates necessity to perform cleaning. As a matter of course, the degree of contamination of the intermediate transfer member depends on the contents of an image which the liquid-development electrophotographic apparatus B05 forms. Thus, an operator must monitor the conditions of printing media ejected from the liquid-development electrophotographic apparatus B05 and set an appropriate timing of performing cleaning.
In Step S51, the operator selects a cleaning mode as an operation mode of the liquid-development electrophotographic apparatus B05. This causes the arithmetic control section B50 to fetch a program segment associated with the cleaning mode from the control program section B58 and to execute the program segment.
In Step S52, the development control section B56b retreats the image formation section B52. Specifically, this retreat operation causes the developing units 54, 55, 56, and 57 and the carrier-removing unit 58 to separate from the intermediate transfer member 51.
In Step S53, the printing control section B56a retreats the printing drive section B51. Specifically, this retreat operation causes the backup roller 59 to separate from the intermediate transfer member 51.
In Step S54, the arithmetic control section B50 starts a cleaning operation. Specifically, in this cleaning operation, the intermediate transfer member 51 rotates for a predetermined period of time while remaining in contact with the cleaning unit 52.
In Step S55, the arithmetic control section B50 ends the cleaning operation. Then, proceeding to Step S56, the arithmetic control section B50 cancels the retreat operation of the image formation section B52 and the retreat operation of the printing drive section B51 performed for the cleaning mode. Then, proceeding to Step S57, the arithmetic control section B50 stands by in preparation for the subsequent image formation mode.
As described above, since the degree of contamination of the intermediate transfer member depends on the contents of an image which the liquid-development electrophotographic apparatus forms, an operator must monitor the conditions of printing media ejected from the liquid-development electrophotographic apparatus and set appropriate cleaning conditions.